This invention relates generally to subsea oil and gas production methods and apparatus and, more particularly, to a crossover christmas tree system.
It is conventional practice to complete a subsea well with a multi bore tubing hanger with tubing suspended below. One bore is a production bore of between 5 and 10 inches nominal diameter and the other is a smaller annulus bore of about 2 inches. The tubing hanger and the associated tubing are run into a subsea wellhead on a running assembly comprising a tubing hanger running tool and a multi bore riser until the tubing hanger is landed and sealed in a wellhead housing. The wellhead carries a blowout preventor (BOP) stack which is connected to a marine riser through which the tubing hanger is run.
This configuration, with the bores side-by-side is typical because it is relatively simple to seal off the bores in the tubing hanger. This is done immediately after the tubing hanger has been landed by running and setting at least one plug into each bore through the multi bore riser used to install the tubing hanger using a wireline technique so that the plugs close the bores and secure the well during the time the tubing hanger is exposed to the ambient environment.
Once the plugs are installed, the multi bore riser is disconnected from the tubing hanger and retrieved to the surface, after which the BOP stack is disconnected from the subsea wellhead and retrieved to the surface with the marine riser. At this point, the tubing hanger is exposed to the ambient environment. The multi bore riser is re-used to run a christmas tree which is landed and locked into the subsea wellhead simultaneously establishing connections to the tubing hanger. The christmas tree is installed using a running assembly comprising the multi bore riser, a safety package including wireline cutting valves and an emergency disconnect package which allows the separation of the surface vessel in the event that it becomes necessary to disconnect the surface vessel from the wellhead. The multi bore riser leads from the upper end of the emergency disconnect package to the vessel. Wirelines can be deployed through the multi bore riser, the safety package and the christmas tree in order to retrieve the plugs in the production bore and the annulus bore. The christmas tree valves are then shut while the safety package and the multi bore riser are retrieved to the surface. The christmas tree is then capped.
In deeper water, the viability of such a conventional multi bore riser is open to question both from structural and commercial viewpoints. In addition, there are many applications in which a larger full bore is desirable. Alternatives to multi bore riser systems utilizing a single bore have been proposed for running and for operating with a christmas tree but, while they can be used for plugging the production bore, they suffer from the problem of providing annulus access with sufficient flow rate capacities to treat a wellxe2x80x94and the lack of annulus flow control.
Further, in deep water it becomes very difficult to align side-valve christmas tree ports with the tubing hanger.
Finally, well drilling and completion operations are very expensive and often based on per hour rig charges. It is desirable to complete wells with a few downhole trips as possible to reduce rig time. In a conventional tubing hanger and christmas tree assembly, the retrieval of the tubing hanger also requires the retrieval of the christmas tree. It would be desirable and cost efficient to find a system that would allow separate retrieval of the christmas tree and tubing hanger.
The present invention is directed to eliminating, or at least reducing the effect of, one or more of the issues raised above.
The invention is directed to a style of christmas tree wherein the tubing hanger is landed in the wellhead, and both the tree and the tubing hanger can be removed independently. This independent ability to retrieve either the tree or the tubing hanger, as required, is achieved through the use of a crossover piece in the tree. When installed, the crossover piece directs the flow of the production fluid to the production valves outside the tree, and directs the flow of fluids to or from the tubing annulus. When the crossover piece is removed, full-bore access through the tree is available, and the tubing hanger, landed below the tree can be removed with the tree in place
One exemplary embodiment of the present invention encompasses a subsea oil or gas well assembly. Such an embodiment includes: a wellhead; a christmas tree coupled to the wellhead; and a tubing hanger landed within the wellhead. A sliding valve is disposed within the tubing hanger to selectively allow fluid communication between a first port in the sliding valve and a first port in the tubing hanger. A crossover assembly is landed within the tree body, and a crossover stab is disposed within the crossover assembly and adapted to translate the sliding valve between open and closed positions.
A subsea oil or gas well assembly comprising: a wellhead; a christmas tree coupled to the wellhead; and a single bore tubing hanger landed within the wellhead. The tubing hanger includes production tubing suspended from it as should be known in the art. The single bore tubing hanger further includes a plurality of first closable ports which facilitate fluid communication to an annulus defined by the production tubing and an innermost casing.
These and other features of the present invention are more fully set forth in the following description of preferred or illustrative embodiments of the invention.